1. Field of the Invention
The present invention relates to polymers, to products comprising such polymers, and the methods of making and using such polymers and products. In another aspect, the present invention relates to styrenated terpene resin, to products comprising such resin, as well as to methods of making and using such resin and products.
2. Description of the Related Art
Modified terpene resins, such as styrenated terpene resins find use as tackifiers in the adhesive industry, especially the are of hot melt packaging, non-woven, and hot melt pressure-sensitive adhesives. Such resins are co-polymers of a terpene—obtained from pine trees (via sulfate turpentine, a by-product of the Kraft paper manufacturing process or gum turpentine, which is obtained from living pine trees), or obtained from citrus sources, such as orange peels and styrene. The useful terpenes for synthesizing such co-polymers, obtained from pine trees have the general formula C10H16. Typical examples are alpha pinene, beta pinene, Dipentene, and delta-3-carene. A very useful terpene obtained from citrus sources in d-limonene (also C10H16). The styrene-terpene copolymers useful for adhesive applications are predominantly obtained via cationic polymerization of the terpene (or a blend of terpenes) and styrene, using Lewis acid catalysts such as aluminum chloride, aluminum bromide, boron trifluoride, tin chloride, titanium chloride, ether complexes of boron trifluoride, etc, in a hydrocarbon solvent such as toluene, xylene, naphtha, etc. The typical styrenated terpene resins are solids at ambient temperature and the most useful tackifier resins used in hot melt packaging, non-woven and hot melt pressure sensitive adhesives are those with a softening point (SP) of from about 95 to about 115° C., a weight average molecular weight (Mw) of less than about 2000, a number average molecular weight (Mn) of less than about 1000, and a polydispersity of less than about 2.0. Cationic polymerization processes enable syntheses of styrenated terpene resins with the aforementioned properties. In contrast, free radical or anionic polymerization of styrene and a terpene tends to produce resins with substantially higher MW (e.g. U.S. Pat. No. 5,364,723 mentions syntheses of styrene-myrcene resins with Mw values of greater than 38000 and Mn values greater than 8000 obtained via free radical and anionic polymerization processes), and such resins cannot adequately function as tackifiers in hot melt packaging, non-woven adhesives, or hot melt pressure-sensitive adhesives.
Although styrenated terpene resins can be synthesized using any of the aforementioned terpenes, historically it has been d-limonene or even dipentene (racemic limonene) that has been found to have the most favorable impact on overall reactivity and ease of polymerization of the terpene-styrene system under cationic polymerization conditions. These terpenes facilitate molecular weight (MW) build-up to the desired degree, allow better control of MW, facilitate softening point build-up and control, afford light colored resins, and result in overall excellent yields of the final resin product. When syntheses of styrenated terpene resins are carried out using other terpenes (i.e. alpha pinene, beta pinene, delta-3-carene, etc.) under Lewis acid-catalyzed cationic polymerization conditions, one is confronted with one or more of the following hurdles: difficulty to build up MW and softening point, severe yield loss, excessive MW build-up and therefore an unfavorable impact on resin compatibility in adhesive systems, a strong tendency toward excessive formation of low MW by-products, etc.
The following commercial styrenated terpene resins are available from Arizona Chemical Company:
SYLVARES ® ZT105LT:105° C. softening pointSYLVARES ® ZT106LT:105° C. softening pointSYLVARES ® M 106:105° C. softening point
Each of the resins listed above is produced via cationic polymerization process using a Lewis Acid catalyst. The resins are based on limonene as the major terpene component. The limonene content in all these resins is between 40 and 70% with the CST-derived terpene components constituting 0-30% of the formulations.
The majority of available crude D-limonene in the world is derived from orange peels with Brazilian crude being a major source. The global availability is typically about 60 metric tons, of which about 50% is consumed by the aroma chemicals and solvent/cleaner industries. The crude limonene that is ultimately available for resins is shared between multiple resin producers. The crude limonene is not pure enough to allow its use as a monomer for cationic polymerization processes, and consequently, resin producers refine the crude. Typically, the refined limonene has a 95% or higher purity.
A major portion of the limonene in the world that is available to resin producers is used for the manufacture of styrenated terpene resins. Consequently, there is always the need to buy adequate crude limonene each year to meet sales volumes. However, limonene availability and pricing depends not as much on demand as on the orange crop situation during the particular year. In addition, recently there has been a surge of interest in the use of polyterpene resins based on limonene (co-polymers of limonene and other CST-derived terpenes based on cationic polymerization similar to the styrenated terpene resins) for applications in areas other than traditional uses such as non-wovens. If the volumes of limonene-based polyterpenes for these new uses do grow rapidly, then the availability of styrenated terpene resins for applications in traditional areas would be jeopardized.
In any no/low limonene formulation to synthesize styrenated terpene resins, it would be preferable to employ as large an amount of alpha pinene as possible since this is the most abundant terpene available in most of the CST and Gum Turpentine found in the world. However, cationic polymerization of alpha pinene to produce high softening point and high MW resins is not straightforward under standard conditions of Lewis Acid-catalyzed polymerizations. Standard processes with alpha pinene as the key/sole terpene monomer lead to low yields of solid resin and even at these low yields, the softening points are not very high.
A means of increasing softening point and MW of terpene resins based on high levels, even up to 100%, of alpha pinene via cationic polymerization, is to employ lower polymerization temperatures, typically sub-zero temperatures. Frequently, cationic polymerization processes under such lower reaction temperatures also involve use of modified Lewis acid catalysts instead of conventional Lewis acid catalysts. U.S. Pat. Nos. 3,478,007, 3,622,550, 4,016,346, 4,057,682, and 4,113,653 describe syntheses of 100-115° C. s.p. resins based on alpha pinene as the sole terpene or main terpene in combination with other terpenes or non-aromatic hydrocarbons using such low polymerization temperatures. These patents also describe the preferred use of catalyst systems such as aluminum chloride-trialkylchlorosilanes, aluminum chloride-antimony halides, and aluminum halide-organogermanium halides or alkoxides. However, none of these patents describes the co-polymerization of alpha pinene with a vinylaromatic, such as styrene or alp ha methylstyrene.
A major drawback about the US patents listed above is that they all involve the use of toxic and sometimes very expensive catalyst systems such as antimony halides, trialkylhalosilanes and organogermanium halides and alkoxides. Catalyst removal and/or recovery systems with such processes can also be a hurdle for economic justification for employing such polymerization conditions.